1. Field of the Invention
The present invention relates to a roll stand apparatus for rolling materials with circular or angular profiles, particularly bars and rods.
2. Description of the Related Art
There have been three types of finish rolling apparatuses for bars and rods; a two-roll type in which the two grooved rolls are arranged symmetrically with the center being the pass line of the material to be rolled; a three-roll type in which the three grooved rolls are arranged radially from the pass line with 120-degree intervals, as described in Japanese Patent Examined Publication No. 54-3469; and a four-roll type in which the four grooved rolls are arranged radially from the pass line with 90-degree intervals, as described in Japanese Patent Unexamined Publication No. 63-93403.
The two-roll type of finish rolling apparatus has a simple structure and facilitates the changing of rolls. However, it requires many kinds of finish rolls since the roll grooves at the final finish roll stand must have substantial semicircular profiles. Also, when the materials have slightly different diameters and have to be rolled by the same grooved rolls with the help of a rolling-reduction adjustment, the two-roll type provides poorer rolling precision than the three and four-roll types since such grooves in the two-roll type have smaller relief angles.
The three-roll type of finish rolling apparatus is provided with all-roll drive means and rolling-reduction adjusting means (hereinafter referred to as "parting adjustment means"). Consequently, while all the rolls are driven by one single drive-input shaft, the parting can be adjusted.
The four-roll type of finish rolling device has the largest relief-angles and provides the rolling-precision superior to the three types. The four-roll type is provided with parting adjustment means but not with roll driving means, so that it requires the upstream rolling device to drive materials. With this type, the heads of materials, bars and rods, are likely to be stopped at the roll gap, and high speed (60 to 100 m/s) rolling or narrow material (10 to 5 mm in diameter) rolling is not efficiently carried out. To obtain as much reduction of area as possible, the rolls have to be larger to provide smaller contact angles, which will make the stop more likely.
Recently, rolled bars and rods with high precision are demanded in the market. The demand goes up to a quarter or less of the dimensional tolerance by JIS, e.g. .+-.0.1 mm or less in a diameter of 5.5 to 20 mm. The inventors have aimed at a four-roll rolling mill as the basic concept of a rolling device which is developed to perform high speed rolling and high rolling precision. The conventional four-roll type, as described above, is provided with parting adjustment means but not with roll drive means. Therefore, its features, such as high precision rolling, have not been fully utilized.
The conventional three-roll type provided with the parting adjustment means and the all-roll drive as in Japanese Patent Examined Publication No. 54-3469 has been worked on to be modified into a four-roll type. In such modification, the space for the driving bevel gears is difficult to obtain if four rolls are arranged in accordance with the design of the three-roll type. Or, to obtain the space in the conventional structure, larger rolls inevitably have to be employed to widen the distance between the roll axes, causing a greater rolling reaction force and resulting in a larger roll stand. The conventional three-roll type structure comprising both the parting adjustment means, including planet and sun gears, and the all-roll drive means, including bevel gears, can not be applied to a compact four-roll stand.